Typical mobile communication systems have been developed to provide voice services while guaranteeing user mobility. Such mobile communication systems have gradually expanded their coverage from voice services through data services up to high-speed data services. However, as current mobile communication systems suffer resource shortages and users demand even higher-speed services, development of more advanced mobile communication systems is needed.
Meanwhile, when a data service provider attempts to change HRPD (High Rate Packet Data) based network technology into LTE (Long Term Evolution) based network technology, interworking between the HRPD network and the LTE network is needed in the whole service area of the data service provider until LTE system deployment is completed.
A network operator may permit an eAT (eVolved Access Terminal which supports both HRPD and LTE and may be used interchangeably with a user equipment (UE)) to use an LTE-based service in an area where the LTE network is available and to use an HRPD-based service when LTE service quality is degraded or an LTE signal is unavailable.
For interworking with LTE, the HRPD system provides an eHRPD (evolved HRPD) functionality. The eHRPD functionality has the following merits.                A service available in LTE is made available in both CDMA and LTE by use of CDMA air resources and the LTE core.        Call setup delay is reduced because repetition of interface operation performed with the LTE core at the initial setup time (PPP session setup, subscriber authentication for billing, or the like) is not required regardless of radio-level handover between CDMA and LTE.        It is possible to reuse resources allocated by the LTE core at the initial setup time (IP, PPP session or the like) regardless of movement between CDMA and LTE.        
For data service continuation between LTE and CDMA, a UE remaining in the LTE domain occupies and manages HRPD resources through the LTE wireless network (optimized eHRPD). In the case of HRPD, RAN resources are changed on a subnet basis. To this end, the LTE eNB delivers the subnet ID of the HRPD DO system covering the same area to the UE.
The UE checks the pre-registration zone ID received from the LTE system and, if the value thereof is changed, performs the pre-registration procedure with the target HRPD system.
However, in the event that a UE is placed in an area where multiple HRPD systems overlap each other, whenever a different pre-registration zone ID is received, the UE may have to perform pre-registration with the corresponding HRPD system, repeating unnecessary pre-registration.